The present invention relates to radiation systems and methods and, more particularly, relates to systems and methods for improved radiation dosimetry using a customizable three dimensional (3D) dosimetry phantom.
Radiation as a source for acquiring medical imaging data and delivering therapy has become a mainstay of modern medicine. In either clinical setting, but particularly radiation therapy, radiation is delivered to a defined target volume, generally a specifically designated portion of a patient. In radiation therapy, where the delivered dose is substantially higher than imaging applications, effort is made to deliver the radiation dose in such a manner that the healthy tissue surrounding the target tissues does not receive radiation doses in excess of desired tolerances. In order to achieve this control of the imparted dose to the subject, highly accurate radiation delivery techniques are required. Many factors provide difficulties in obtaining the desired level of accuracy, including differences between the planned and delivered dose distributions and uncertainty in subject position with respect to the treatment system.
Conventional external beam radiation therapy is commonly administered by directing a linear accelerator (“linac”) to produce beams of ionizing radiation that irradiate the defined target volume in a patient. The radiation beam is a single beam of radiation that is delivered to the target region from several different directions, or beam paths. Together, the determination of how much dose to deliver along each of these beam paths constitutes the so-called radiation therapy “plan.” The purpose of the treatment plan is to accurately identify and localize the target volume in the patient that is to be treated. This technique is well established and is generally quick and reliable.
Intensity modulated radiation therapy (“IMRT”) is an external beam radiation therapy technique that utilizes computer planning software to produce a three-dimensional radiation dose map, specific to a target tumor's shape, location, and motion characteristics. IMRT treats a patient with multiple rays of radiation, each of which may be independently controlled in intensity and energy. Because of the high level of precision required for IMRT methods, detailed data must be gathered about tumor locations and their motion characteristics. In doing so, the radiation dose imparted to healthy tissue can be reduced while the dose imparted to the affected region, such as a tumor, can be increased. In order to achieve this, accurate geometric precision is required during the treatment planning stage. Thus, while conventional IMRT methods have had success in increasing the effective dose imparted to the defined target volume while mitigating the imparted radiation dose to the surrounding healthy tissue, further reduction of the radiobiological effect on healthy tissue is desirable.
Image-guided radiation therapy (“IGRT”) employs medical imaging, such as computed tomography (“CT”), concurrently with the delivery of radiation to a subject undergoing treatment. In general, IGRT is employed to accurately direct radiation therapy using positional information from the medical images to supplement a prescribed radiation delivery plan. The advantage of using IGRT is twofold. First, it provides a means for improved accuracy of the radiation field placement. Second, it provides a method for reducing the dose imparted to healthy tissue during treatment. Moreover, the improved accuracy in the delivery of the radiation field allows for dose escalation in the tumor, while mitigating dose levels in the surrounding healthy tissue. The concern remains, however, that some high-dose treatments may be limited by the radiation toxicity capacity of healthy tissues that lay close to the target tumor volume.
However, despite the progressive sophistication in the systems methods for planning and delivering radiation therapy, there is still a substantial potential for the subject to receive undesired radiation doses. In particular, despite the ability to create complex treatment plans where 3D dose distributions are highly customized for each patient, there is a substantial potential for the actual dose delivered to be greater than the planned dose or to be received by the patient in a manner different than that simulated in the plan.
One reason for this undesired potential is a low availability/high cost of systems and methods to verify the radiation dose prior to or during the treatment. Another, more prevalent reason for this undesired potential is a substantial lack of systems and methods that allow for customized measurement and analysis of dose in critical regions of interest.
For example, many of the sophisticated radiation therapy modalities mentioned above feature rotational therapy where it is desirable to use a 3D phantom instead of the very common 2D arrays that are used for static gantry angle IMRT. However, such 3D phantoms generally fall into one of two categories: 3D phantoms coupled with 2D detection arrays and 3D phantoms coupled with 3D detection systems.
In a first case, some have attempted to employ commonly-available 2D radiation detection arrays inserted into fixed “3D” phantoms. In these cases, though the phantom extends along the three planes (sagittal, coronal, and transverse) corresponding to those planes of a subject, due to the use of a 2D detection array, these systems are only capable of measuring dose along the one plane along which the 2D detection array extends. Furthermore, these systems are plagued by inaccuracies associated with problems of angular dependence. That is, it is known that the 2D detection arrays have a substantial change in sensitivity with variations in the angle of incidence of radiation on the 2D detection array. Thus, the angular dependence of the 2D detection array limits the accuracy of these systems.
Some have recognized the limitations of these systems combining 3D phantoms with 2D detection arrays and, in a second case, have developed 3D dosimetry arrays that are combined with 3D phantoms in a fixed dose detector arrangement. However, these systems are expensive and have limited, if not entirely very unsuitable, detector placement. Thus, though such systems are quite sophisticated, they still present substantial limits on practical clinical use in per-patient dose quality assurance (QA).
It would therefore be desirable to provide a system and method for QA in radiation dosimetry that provides greater flexibility without increases in overall system costs or complexity.